Bone density varies between races and by gender. Blacks and men tend to have higher bone densities than whites and women. Lately, estrogen metabolism has slowly gained recognition as an important determinant of bone density in postmenopausal women. Because recent reports suggest that estrogen is likewise important to skeletal health in men as it is in women, we believe that estrogen metabolism also plays a critical role in bone loss and bone maintenance in men. We propose that differences in estrogen metabolism may account for gender and racial differences in bone density. Furthermore, we hypothesize that this variability in estrogen metabolism is due to CYP gene polymorphisms of the key enzymes that metabolize estrogen resulting in variants that have altered enzyme activity affecting the balance between inactive and active estrogen metabolites. To date there is very limited proof, mostly in-vitro, that these variants have altered catalytic function. This proposal would serve to fill in this gap in knowledge and establish the biological significance of CYP gene polymorphism on enzyme activity and bone density in the elderly. The primary aims of this proposal are 1) to determine the prevalence of gene polymorphism of CYP1A1, CYP1B1, CYP1A2 and CYP3A4 among women and men of different ethnic groups 2) to determine the functional correlates of polymorphisms of the above-mentioned genes on estrogen status and bone density. This is a cross-sectional study of postmenopausal women and men 50 years of age or over, the population who are at highest risk for bone loss and osteoporosis. We intend to establish the CYP genotypes that are over-represented in a particular population and evaluate the functional status of the different variants by measuring urinary estrogen metabolites. Although it is not considered a primary goal, we will also measure bone mineral density and test the hypothsesis that variants that preferentially shifts estrogen metabolism to the inactive pathway is associated with a lower bone density and vice -versa. These data will be used to develop a full proposal and test the long-term hypothesis that CYP 450 enzyme gene polymorphism is important for bone mass maintenance and bone loss in elderly men and women. Another long-term goal is to extend evaluation to the younger population, to determine if polymorphisms of the CYP genes are important determinant of peak bone mass.